1. Field of the Invention
The present invention relates to a solenoid driving device which drives and controls an actuator by using a solenoid and an active vibration isolating support device which is equipped with the solenoid driving device and elastically supports an engine in a vehicle body.
2. Description of the Related Arts
Japanese Unexamined Patent Application Publication No. 2008-057559 discloses an active vibration isolating support device.
The active vibration isolating support device disclosed in Japanese Unexamined Patent Application Publication No. 2008-057559 includes an ACM (Active Control Mount) controlling ECU (corresponding to a component referred to as “a control unit” in the present invention) and an active control mount. The ACM controlling ECU is communicatively connected to an engine controlling ECU (Electric Control Unit). The engine controlling ECU controls the operation of fuel injectors of the engine based on a crank pulse signal and a TDC (Top Dead Center) pulse signal. The engine controlling ECU also switches to select an all cylinder operation state or selective-cylinder operation states by controlling the operation of the hydraulic actuators of the valve resting mechanism of the engine. Since an engine vibration is different among the all cylinder operation state and the selective-cylinder operation states, the ACM controlling ECU receives the crank pulse signal, the TDC pulse signal and a cylinder stop signal which indicates to stop a cylinder from the engine controlling ECU. The ACM controlling ECU determines an engine vibration cycle such as a vibration mode of primary vibration, 1.5th order vibration or secondary vibration, and calculates the amplitude or the phase of the engine vibration to optimally control the active control mount in accordance with the engine vibration state.
Japanese Unexamined Patent Application Publication No. 2007-269049 discloses an active vibration isolating support device which optimally controls an active control mount in a motor-assisted hybrid vehicle based on the operation state of the motor vibration control. The active vibration isolating support device disclosed in Japanese Unexamined Patent Application Publication No. 2007-269049 includes a control map changer for changing a phase correction control map for generating a target current waveform for vibration control of an engine mount depending on the presence/absence of a motor vibration control signal which is supplied to a generator motor. Accordingly, optimum active mount control based on the state of vibration control by the generator motor can be performed.
There has been known a hybrid vehicle including a motor generator for assisting an engine output and an engine which can perform a selective cylinder operation. Since an acceleration function realized by the motor assist is added to the hybrid vehicle, the hybrid vehicle can perform the selective-cylinder operation in a vehicle speed range higher than a vehicle speed range in which a selective-cylinder operation state can be performed by a conventional vehicle (not a hybrid vehicle) which includes an engine capable of performing a selective cylinder operation.
If a selective-cylinder operation is performed in a vehicle speed range higher than the vehicle speed range allowed in the conventional vehicle, the amplitude of the engine vibration becomes greater. Therefore, in order to enhance the vibration absorbing property of the active control mount, the ACM controlling ECU is provided with a booster circuit for boosting the driving voltage supplied to an actuator of the active control mount to, for example, 24V from the battery voltage to realize a displacement of an active control mount which cancels out the increased amplitude of the engine vibration (see Japanese Patent Application Publication No. 2005-249013).
An actuator of the active control mount according to Japanese Patent Application Publication No. 2008-057559 is driven by a solenoid magnet (corresponding to a coil assembly 43). In accordance with the variation of the drive frequency for cancelling out the engine vibration, a voltage required for supplying the same strength of the driving current becomes higher as the drive frequency is increased because the driving current for driving the solenoid magnet needs to be supplied against the counter-electromotive voltage of the solenoid magnet.
Therefore, in a conventional active vibration isolating support device with an active control mount, as shown in FIG. 6A, the maximum voltage Vmax is set in advance at which the maximum value IRq of the target current waveform of a driving current required in a high range of the drive frequency fDV [Hz] can be supplied to the solenoid magnet. A booster circuit then boosts the battery voltage VB to the maximum voltage Vmax and supplies a driving circuit which performs the PWM (Pulse Width Modulation) control with the electricity to be supplied to the solenoid magnet.
In the above configuration, however, the booster circuit disadvantageously boosts the battery voltage to Vmax even in a range where the drive frequency fDV [Hz] is low, for example, at the drive frequency f1 [Hz] where V1 is satisfactory as the required voltage value VRq for supplying the maximum value IRq of the target current waveform of a required driving current (i.e. the maximum target current value I1) as shown in FIG. 6B. Thus, the electric power of W1′ which is greater than W1 is supplied as the required electric power WRq for driving the solenoid magnet. This causes a problem that the excessive electric power (W1′-W1) is consumed by the booster circuit or the driving circuit wastefully generating heat, which deteriorates an electric power efficiency.
Since the ACM controlling ECU is provided with the booster circuit, the electric power consumption becomes larger, and the amount of the heat generated by the booster circuit or the driving circuit which supplies electricity to the actuator of the active control mount by PWM control is increased. This causes a need for heat radiation and cooling. Especially, when the ACM controlling ECU is arranged in a vehicle compartment of a vehicle and the vehicle is left for a while without any passengers on the vehicle in the idling driving state of the engine, heat radiated from the ACM controlling ECU may not be fully removed.